This application is not related to any pending United States or international patent application.
This application is not referenced in any Microfiche Appendix.
The invention to which this disclosure pertains is an apparatus for tapping a hole in a pipeline and it is particularly adapted for use as a subsea tapping machine. The invention is specifically applicable for use in diverless subsea tapping operations.
Tapping machines have been used for drilling holes in the sidewall of pipelines in which the pipeline is under liquid or gas pressure since at least 1971 when U.S. Pat. No. 3,614,252 entitled, xe2x80x9cTapping Apparatusxe2x80x9d was granted. This patent discloses a tapping apparatus that includes a supporting assembly affixed to the exterior of a pipeline, a feed screw mounted on the supporting assembly for rotation around its longitudinal axis, a boring bar connected to the feed screw for axial movement relative to the boring bar upon relative rotation of the feed screw and bar, a cutter connected to the boring bar for rotation by the boring bar and for rotatably engaging the external surface of a pipeline by which a hole is cut into the pipeline. The relative rotational speed of the boring bar and feed screw are employed to control the axial advancement or retraction of the boring bar and, correspondingly, the hole cutter. This patent further describes a system for controlling the relative speed of rotation of the boring bar and adjust the rate the feed screw moves the boring bar and the cutter in proportion to the load applied to the cutter.
The tapping apparatus disclosed in U.S. Pat. No. 3,614,252 is designed for use on the earth""s surfacexe2x80x94that is, was not specifically designed for use underwater. However, U.S. Pat. No. 4,579,484 entitled, xe2x80x9cUnderwater Tapping Machinexe2x80x9d that issued on Apr. 1, 1986 provides a machine that is specifically useful in tapping a hole in a pipeline in which the pipeline is submerged in water. This patent describes changes in the tapping machine of U.S. Pat. No. 3,614,252 that are required to accommodate the pressure applied by a water environment such as when tapping a hole in a pipeline in a lake, in the bottom of a river or in an ocean. Specifically, U.S. Pat. No. 4,579,484 describes how pressures are balanced between the exterior and the interior of a tapping machine in an underwater environment.
A substantial force can be imposed on a tapping apparatus when the circular drill penetrates the wall of the pipeline under pressurexe2x80x94that is, when the pressure within the pipeline is applied to the interior of the tapping machine. Tapping a pipeline under pressure is frequently referred to as xe2x80x9chot tappingxe2x80x9d. To alleviate these high forces U.S. Pat. No. 5,439,331 that issued on Aug. 8, 1995 entitled, xe2x80x9cHigh Pressure Tapping Apparatusxe2x80x9d provides a means to control the hydraulic fluid pressure inside the tapping machine body based upon the pipeline pressure so that the pressure inside the pipeline body can be increased or decreased as required to at least substantially counterbalance the pressure encountered when the wall of a high pressure pipeline is penetrated.
U.S. Pat. No. 6,012,878 entitled, xe2x80x9cPressure Balanced Subsea Tapping Machinexe2x80x9d that issued on Jan. 11, 2000 provides further refinements in the technology of counterbalancing internal and external pressures encountered by a tapping machine when tapping a high pressure subsea pipeline. That is, this patent teaches techniques to counterbalance not only the great ambient pressures encountered in tapping a subsea pipeline but also provides for counterbalancing the high pressures encountered internally when the pipeline wall is penetrated.
These four mentioned previously issued U.S. Patentsxe2x80x94that is, U.S. Pat. Nos. 3,614,252, 4,579,484, 5,439,311 and 6,012,858 are all specifically related to pipeline tapping machines and the later issued ones to pipeline tapping machines used underwater. These four patents form a good background for the improvements contained in the present disclosure. These four patents including the drawings and descriptions therein are incorporated herein by reference as if repeated verbatim and as if the drawings were part of the drawings of the present disclosure in this application.
For additional information relating to subsea tapping operations and to the general area of maintaining, repairing and tapping onto submerged pipelines, reference may be had to the following previously issued United States patents:
Because of the almost insatiable demand for petroleum in the world today, more and more production occurs off-shorexe2x80x94that is, in the ocean. As exploration and production moves to deeper water, transporting newly found gas and oil economically becomes a key factor in determining the profitability of deep water exploration. Underwater pipelines have been installed in older fields. When new production is found in adjacent oil fields, substantial savings can be obtained by routing production to existing lines but only if the existing lines can be tapped and especially, only if the existing lines can be tapped while under pressurexe2x80x94that is, without interfering with current production.
When underground pipelines exist at relatively shallow depths, underwater tapping operations can be very successfully carried out by the use of divers. However, as working depths increase, the use of divers becomes more and more impractical. Therefore, a need has developed for subsea tapping machines that can be operated without the benefit of a diver. The invention of the present disclosure is particularly related to a subsea tapping machine that is specifically adaptable for diverless operation. This is not to mean that the principles of the present invention are limited to diverless subsea tapping machines as such principles may be employed even if a diver is present or some of the principles of the invention disclosed herein may be applicable for designing and developing improved tapping machines for use on-shore, however by and large, the present invention is particularly adaptable for diverless subsea tapping machine operations.
Hot tapping is a well proven and established technology whereby a new smaller or equal size pipeline can be joined into an existing pipeline while the existing pipeline is on-line and operating at full pressure and temperature. Hot taps are completed by installing a mechanical clamp fitted with elastomeric seals around the pipeline. A branch outlet on the mechanical clamp is fitted with a block valve to form a control outlet. The mechanical clamp seals around the pipeline and the block valve isolates the pressure once a hole is cut in the pipeline. A tapping machine is attached to the block valve. The block valve is opened to allow the tapping machine cutter to contact the pipeline and to cut a hole in it. After cutting a hole in the pipeline, the cutter is withdrawn through the valve and the valve is blocked in. The branch is then ready for a tie-in.
Subsea mechanical hot tap clamps typically use elastomeric elements to form a seal around a pipeline. The hot tap clamp is a split sleeve-type clamp that forms an annulus around the pipeline. The sealing system typically utilizes circumferential packers and longitudinal seals to form a pressure boundary around a pipeline. A structural branch connection is either welded or machined into one clamp half as fitted to provide a tie-in point. The branch connection is fitted with a block valve which functions as a pressure boundary control point to the trunk line.
The tapping machine is attached by use of a flange to the block valve. The typical subsea hot tapping machine is a hydraulic mechanical machine operated by a diver. Once a hole is cut, the cutter head is retracted back through the valve, the valve is shut in, and the hot tapping machine is removed.
The basic steps required for a typical subsea hot tap of a pipeline are as follows;
a) locate the pipeline;
b) excavate around the pipeline where the hot tap is to occur;
c) initial inspection of pipeline for field joints and longitudinal weld seams;
d) clean the pipeline of coatings to bare metal;
e) measure the pipeline for tolerances acceptable for hot tap clamp installation;
f) rig and deploy a hot tap clamp;
g) conduct pressure tests to verify that no leaks exist between the hot tap clamp and the exterior of the pipeline;
h) affix a valve, typically a ball valve, to the hot tap clamp;
i) affix a hot tap machine to the valve;
j) tap the pipeline;
k) withdraw the tapping machine boring bar and close the valve;
l) remove the tapping machine from the valve;
m) affix a branch connection to the valve; and
n) open the valve to provide communication between the interior of the pipeline and the interior of the branch connection.
As can be seen from the summary procedure above, subsea hot tapping requires substantial bottom time by divers. Diver intervention is not feasible in water depths in excess of about 1,000 feet. Below about 1,000 feet of water, a remote operating vehiclexe2x80x94that is, an underwater robotic device controllable from the earth""s surface is the most feasible way of performing hot tapping operations.
In the Gulf of Mexico, approximately 60% of all new pipelines scheduled for installation in the next three years are in water depths greater than 2,000 feet. Tying into closer existing pipelines could reduce the cost of installing many of these pipelines. In some locations, provisions have been made to allow for a tie-in by means of a lateral Tie-In Sled or Pipeline End Manifold. In many locations however, this equipment is not available and the only option is to complete a hot tap tie-in.
The apparatus for tapping a hole in a pipeline of this disclosure is characterized by one or more of the following improvements in existing tapping machine technology:
a) A centrally located flange for adapting the tapping machine to different pipeline sizes and that allows for use of different length spool pieces and accommodates varying lengths/diameters of tapping valves and collet connectors while minimizing travel requirements for the tapping machine.
b) A linear position indicator extending down the center of the tapping machine to provide an electronic signal that indicates the boring bar position.
c) Rotational speed transducers providing feed screw and boring bar revolutions per minute data from which feed rate and the position of the boring bar can be calculated. These transducers sense rotation from magnet wheels located behind the feed and drive motors and provide a reliable means for determining feed and drive rotational speed for use in calculating and setting tapping parameters.
d) A pilot drill with spring loaded positive retention latches to capture coupons and for providing a redundant and positive coupon retention method which still allows the tapping machine to be removed even if the tap is partway completexe2x80x94that is, the coupon is not completely cut from the pipeline.
e) A circular cutter with hard-faced teeth rather than the typically brazed or mechanically attached teeth used with existing tapping machines to provide a system for cutting higher than normal strength pipeline efficiently while minimizing the possibility of a loose tooth causing excessive cutter damage or failure to complete a tap.
f) A remote mechanical feed screw override that can be connected with a remote operating vehicle to allow emergency retraction of the boring bar and removal of the tapping machine or completion of a tap in the case of partial or total hydraulic failure.
g) A boring bar accumulator that equalizes the tapping machine internal pressure to seawater pressure initially and then equalizes tapping machine internal pressure to pipeline pressure after the pilot drill penetrates the pipeline to thereby prevent applying a pressure load from the pipeline to the tapping machine drive threads.
h) A relief valve to relieve pressure as the boring bar is retracted in the event the piston in the boring accumulator becomes stuck or pressure builds up because of a leak to thereby insure that the boring bar can be retracted and the tapping machine recovered in the event of a failure in the pressure balancing system.
i) A motor housing accumulator to equalize pressure to the subsea pressure to keep from damaging the hydraulic motors from high external pressure in deep water and further to insure a redundant and more reliable pressure balancing and over-pressure protection for deep water applications by protecting the hydraulic motors and other components of the tapping machine.
j) A check valve to allow seawater into the motor housing in the event of a seal leak that permits motor housing pressure to fall below the sea pressure to insure a redundant and therefore more reliable pressure balancing and over-pressure protection system for protecting the hydraulic motors and components in the tapping machine in the event of a balancing system failure.
k) A relief valve to relieve pressure in the motor housing in the event of a seal leak that permits the motor housing pressure to rise above the sea pressure to ensure redundant and therefore more reliable pressure balancing and over-pressure protection for protecting the hydraulic motors and components in the tapping machine in the event of balancing system failure.
l) A hydraulic counterbalance valve to limit feed motor overrunning to ensure adequate independent control of the feed and drive speeds while using a single hydraulic power source. Frictional forces generated by the seals in the drive tube when subjected to high pressures tend to rotate the feed motor when the drive motor is turning. The counterbalance valve is a normally open valve that is closed when pressure on the downstream stream side of the feed motor is high compared with the feed motor upstream pressure. Overrunning is the tendency of one motor to rotate because of rotation of another motor.
m) A digital remote control system including read-outs of pressures at the drive motor, the feed motor and the motor housing and at both sides of the boring bar accumulator. The feed motor and drive motor rotational speeds are monitored using rotational speed sensor outputs. The boring bar position is monitored directly by reading the linear transducer output and indirectly by calculating the boring bar position using the rotational speed transducer outputs and the known relationship between the motor speed and feed rate. The boring bar accumulator piston position is also monitored to check for malfunctions in the compensation system to thereby effectively control tapping machine functions while providing operating condition information to the operator sufficient to properly complete a tap from a very remote location and to diagnose and resolve problems.
The tapping machine of this disclosure is designed to operate at underwater depths previously unachievable when the use of a diver was mandated. The tapping machine of this disclosure is able to operate at a maximum depth of 10,000 feet of seawater, well beyond the current limits of human divers. The machine is remotely operated from the surface. Taps may range in size from 6 inches to 20 inches or larger and work with a maximum pipeline operating pressure of 3705 psi whether operating on land or at depth of up to 10,000 feet of seawater.
The tapping machine is mounted into a support and alignment frame to prepare it for subsea use. The mating half of the collet connector is attached to the tapping machine while it is in the frame. The frame is lowered until the opposed halves of the collet connector mate. Seawater is purged from the fitting. A subsea power unit/tool control module mates with the machine and provides the hydraulic power and the electronic communication circuits required to operate and monitor the tapping machine. A technician operates and monitors the tapping machine from the surface using remote control technology. To assist the technician, the machine itself is designed to prevent cutter stalls through a self-adjusting load sensing circuit to relieve the cutter feed rate during difficult tapping operations. A self-activating pilot ensures positive coupon retention during tapping operations. Upon completion of a tap, the cutter is retracted and the tapping machine is retrieved to the surface.
The tapping machine herein employs a number of systems to ensure reliable operation and to provide feedback to the technician. These include:
a) a linear transducer used to monitor the exact boring bar position during a tap;
b) sensors to monitor the rotation of the boring bar and feed screw and for use in calculating boring bar position as a redundant system to the linear transducer;
c) a pressure balancing accumulator to balance the pressure across the boring bar to relieve stress on the feed and drive systems during the tapping operation;
d) a motor housing balancing system having an accumulator used to balance the pressure in the motor housing with the sea pressure to ensure reliable motor operation;
e) check and relief valves to ensure that the pressure in the motor housing and the pressure balancing circuits remain within acceptable limits;
f) accumulator pressure/position sensors to ensure proper operation of the balancing accumulators and monitor the volume displacement in the accumulators;
g) hydraulic system pressure monitors to indicate the loading on the system; and
h) a counterbalance valve for preventing overrunning of the feed motor by the drive motor.